[svsadatia]

I am doing coal combustion analysis in Furnace of actual scale.I want to solve it in Ansys CFX. I am new in this combustion era but i have studied most of fundamental theory regarding combustion.My questions are listed below:

1) How to find out which reaction model is appropriate for my coal(used in problem) ?
2) I have solved coal combustion problem ..now i want to use the same setup and boundary condition for different geometry than solved one ..but new geometry is very large compared to solved one..then does it make physical model of problem inappropriate ?